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Message-ID: <1305619677.2850.11.camel@edumazet-laptop>
Date: Tue, 17 May 2011 10:07:57 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Benoit Sigoure <tsunanet@...il.com>
Cc: davem@...emloft.net, kuznet@....inr.ac.ru, pekkas@...core.fi,
jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tcp: Expose the initial RTO via a new sysctl.
Le mardi 17 mai 2011 à 00:40 -0700, Benoit Sigoure a écrit :
> Instead of hardcoding the initial RTO to 3s and requiring
> the kernel to be recompiled to change it, expose it as a
> sysctl that can be tuned at runtime. Leave the default
> value unchanged.
>
I wont discuss if introducing a new sysctl is welcomed, only on patch
issues. I believe some work in IETF is done to reduce the 3sec value to
1sec anyway.
> Signed-off-by: Benoit Sigoure <tsunanet@...il.com>
> ---
> Documentation/networking/ip-sysctl.txt | 6 ++++++
> include/linux/sysctl.h | 1 +
> include/net/tcp.h | 3 ++-
> kernel/sysctl_binary.c | 1 +
> net/ipv4/syncookies.c | 2 +-
> net/ipv4/sysctl_net_ipv4.c | 11 +++++++++++
> net/ipv4/tcp.c | 4 ++--
> net/ipv4/tcp_input.c | 8 ++++----
> net/ipv4/tcp_ipv4.c | 6 +++---
> net/ipv4/tcp_minisocks.c | 6 +++---
> net/ipv4/tcp_output.c | 2 +-
> net/ipv4/tcp_timer.c | 9 +++++----
> net/ipv6/syncookies.c | 2 +-
> net/ipv6/tcp_ipv6.c | 6 +++---
> 14 files changed, 44 insertions(+), 23 deletions(-)
>
> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> index d3d653a..c381c68 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -384,6 +384,12 @@ tcp_retries2 - INTEGER
> RFC 1122 recommends at least 100 seconds for the timeout,
> which corresponds to a value of at least 8.
>
> +tcp_initial_rto - INTEGER
> + This value sets the initial retransmit timeout, that is how long
> + the kernel will wait before retransmitting the initial SYN packet.
> +
> + RFC 1122 says that this SHOULD be 3 seconds, which is the default.
> +
units ? seconds ? ms ? jiffies ? I suggest using ms as external
interface.
> tcp_rfc1337 - BOOLEAN
> If set, the TCP stack behaves conforming to RFC1337. If unset,
> we are not conforming to RFC, but prevent TCP TIME_WAIT
> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
> index 11684d9..96a9b41 100644
> --- a/include/linux/sysctl.h
> +++ b/include/linux/sysctl.h
> @@ -425,6 +425,7 @@ enum
> NET_TCP_ALLOWED_CONG_CONTROL=123,
> NET_TCP_MAX_SSTHRESH=124,
> NET_TCP_FRTO_RESPONSE=125,
> + NET_IPV4_TCP_INITIAL_RTO=126,
We dont add new values here anymore, only anonymous ones.
> };
>
> enum {
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index cda30ea..a2bb0f1 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -213,6 +213,7 @@ extern int sysctl_tcp_syn_retries;
> extern int sysctl_tcp_synack_retries;
> extern int sysctl_tcp_retries1;
> extern int sysctl_tcp_retries2;
> +extern int sysctl_tcp_initial_rto;
> extern int sysctl_tcp_orphan_retries;
> extern int sysctl_tcp_syncookies;
> extern int sysctl_tcp_retrans_collapse;
> @@ -295,7 +296,7 @@ static inline void tcp_synq_overflow(struct sock *sk)
> static inline int tcp_synq_no_recent_overflow(const struct sock *sk)
> {
> unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
> - return time_after(jiffies, last_overflow + TCP_TIMEOUT_INIT);
> + return time_after(jiffies, last_overflow + sysctl_tcp_initial_rto);
> }
>
> extern struct proto tcp_prot;
> diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
> index 3b8e028..d608d84 100644
> --- a/kernel/sysctl_binary.c
> +++ b/kernel/sysctl_binary.c
> @@ -354,6 +354,7 @@ static const struct bin_table bin_net_ipv4_table[] = {
> { CTL_INT, NET_IPV4_TCP_KEEPALIVE_INTVL, "tcp_keepalive_intvl" },
> { CTL_INT, NET_IPV4_TCP_RETRIES1, "tcp_retries1" },
> { CTL_INT, NET_IPV4_TCP_RETRIES2, "tcp_retries2" },
> + { CTL_INT, NET_IPV4_TCP_INITIAL_RTO, "tcp_initial_rto" },
no need here. sysctl() is deprecated.
> { CTL_INT, NET_IPV4_TCP_FIN_TIMEOUT, "tcp_fin_timeout" },
> { CTL_INT, NET_TCP_SYNCOOKIES, "tcp_syncookies" },
> { CTL_INT, NET_TCP_TW_RECYCLE, "tcp_tw_recycle" },
> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
> index 8b44c6d..089bc92 100644
> --- a/net/ipv4/syncookies.c
> +++ b/net/ipv4/syncookies.c
> @@ -186,7 +186,7 @@ __u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
> * sysctl_tcp_retries1. It's a rather complicated formula (exponential
> * backoff) to compute at runtime so it's currently hardcoded here.
> */
> -#define COUNTER_TRIES 4
> +#define COUNTER_TRIES (sysctl_tcp_initial_rto + 1)
Are you sure of this ?
If HZ=1000, sysctl_tcp_initial_rto is 3000
COUNTER_TRIES goes from 4 to 3004
> /*
> * Check if a ack sequence number is a valid syncookie.
> * Return the decoded mss if it is, or 0 if not.
> diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
> index 321e6e8..24dc21d 100644
> --- a/net/ipv4/sysctl_net_ipv4.c
> +++ b/net/ipv4/sysctl_net_ipv4.c
> @@ -30,6 +30,8 @@ static int tcp_adv_win_scale_min = -31;
> static int tcp_adv_win_scale_max = 31;
> static int ip_ttl_min = 1;
> static int ip_ttl_max = 255;
> +static int tcp_initial_rto_min = TCP_RTO_MIN;
warning its jiffies units here.
> +static int tcp_initial_rto_max = TCP_RTO_MAX;
>
> /* Update system visible IP port range */
> static void set_local_port_range(int range[2])
> @@ -246,6 +248,15 @@ static struct ctl_table ipv4_table[] = {
> .mode = 0644,
> .proc_handler = proc_dointvec
> },
> + {
> + .procname = "tcp_initial_rto",
> + .data = &sysctl_tcp_initial_rto,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = proc_dointvec_minmax,
so unit is jiffies ? Really its not a good thing. Use ms instead.
Consider proc_dointvec_ms_jiffies(), here.
> + .extra1 = &tcp_initial_rto_min,
> + .extra2 = &tcp_initial_rto_max,
> + },
> {
> .procname = "tcp_fin_timeout",
> .data = &sysctl_tcp_fin_timeout,
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index b22d450..e9e7c3f 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2352,7 +2352,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
> case TCP_DEFER_ACCEPT:
> /* Translate value in seconds to number of retransmits */
> icsk->icsk_accept_queue.rskq_defer_accept =
> - secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
> + secs_to_retrans(val, sysctl_tcp_initial_rto / HZ,
Here you assume sysctl_tcp_initial_rto is expressed in jiffies ?
Oh well...
> TCP_RTO_MAX / HZ);
> break;
>
> @@ -2539,7 +2539,7 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
> break;
> case TCP_DEFER_ACCEPT:
> val = retrans_to_secs(icsk->icsk_accept_queue.rskq_defer_accept,
> - TCP_TIMEOUT_INIT / HZ, TCP_RTO_MAX / HZ);
> + sysctl_tcp_initial_rto / HZ, TCP_RTO_MAX / HZ);
> break;
> case TCP_WINDOW_CLAMP:
> val = tp->window_clamp;
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index bef9f04..39f6c27 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -890,7 +890,7 @@ static void tcp_init_metrics(struct sock *sk)
> if (dst_metric(dst, RTAX_RTT) == 0)
> goto reset;
>
> - if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
> + if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (sysctl_tcp_initial_rto << 3))
Here you assume jiffies unit again. I wonder how this was tested :(
Please fix this and chose a definitive unit.
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